Simon Napper reports on a double skin façade research project

With schemes for incorporating natural ventilation into new commercial buildings, the use of double skin façades is becoming more popular. But their introduction has not been universally successful. Harris Poirazis of Lund University describes the double skin façade as: “a system consisting of two glass skins placed in such a way that air flows in the intermediate cavity. The ventilation of the cavity can be natural,
fan-supported or mechanical. The glass skins can be single or double glazing units with a distance from 20cm up to 2 metres. Often, for protection and heat extraction reasons during the cooling period, solar shading devices are placed inside the cavity.”

The recent interest in double-skin façades is due to increasing environmental concerns in architecture and the demand by consumers for more of a green image in the buildings they rent or own, says Poirazis.

The EU’s SAVE programme (which supports energy efficiency schemes) has been funding a project called Bestfacade. This is now nearing completion and is designed to promote best practice in this technology. The results are featured on the project’s website (which seems to be running a bit behind schedule as some of the documentation has not yet been loaded onto the website).

The project group has spent the last 18 months looking at the technology and developing a simple, common assessment method for the different varieties of double skin façade. While this form of building has become an increasingly popular option for office buildings over the past 15 years, not all of them perform well. “Far from it,” says the project report, “In most cases large air conditioning systems have to compensate for summer overheating problems and the energy consumption badly exceeds the intended heating energy savings.” Hence the need for a central store of best practice information.

The main features of the project include:

• an information system database containing details and performance data collected from a survey of double skin facades built in the European Union
  
• a design guide including best practice examples, providing basic scientific, technical and economic knowledge on double skin façades
  
• an assessment method to measure the thermal behaviour and energy performance, and which can be integrated with the assessment methods of the Energy Performance of Buildings Directive (EPBD).
  This calculation procedure should harmonise with the currently developed CEN standards for the implementation of the EPBD say the project report. The method is provided as an information tool on the project website for the simple assessment of the energy performance of different façade types
  
• benchmarks to allow users and operators to compare their energy consumption levels with others in the same group, set future targets and identify measures to reduce energy consumption
  
•  an overview of existing non-technical barriers to implementation with suggested solutions to overcome them.
  
  The results are all on (or in the process of being installed on) the project website at:
  www.bestfacade.com